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An “Iceberg” Coating Preserves Bulk Hydration Dynamics in Aqueous PEG Solutions
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2017-11-13 00:00:00 , DOI: 10.1021/acs.jpcb.7b08030
Kimberly R. Daley 1 , Kevin J. Kubarych 1
Affiliation  

Ultrafast picosecond time scale two-dimensional infrared (2D-IR) spectroscopy of a new water-soluble transition metal complex acting as a vibrational probe shows that over a range of concentration and poly(ethylene glycol) (PEG) molecular mass (2000, 8000, and 20000 Da) the time scale of the sensed hydration dynamics differs negligibly from bulk water (D2O). PEG is well-known to establish a highly stable hydration shell because the spacing between adjacent ethereal oxygens nearly matches water’s hydrogen-bonding network. Although these first-shell water molecules are likely significantly retarded, they present an interface to subsequent hydration shells and thus diminish the largely entropic perturbation to water’s orientational dynamics. In addition to the longer PEGs, a series of concentration-dependent 2D-IR measurements using aqueous PEG-400 show a pronounced hydration slowdown in the vicinity of the critical overlap concentration (c*). Comparison between these dynamical results and previously reported steady-state infrared spectroscopy of aqueous PEG-1000 solutions reveals a strikingly identical dependence on number of water molecules per ethylene oxide monomer, scaled according to the critical overlap concentration.

中文翻译:

“冰山”涂层保留了PEG水溶液中的大体积水合动力学

一种新型的用作振动探针的水溶性过渡金属络合物的超快皮秒时标二维红外(2D-IR)光谱显示,在一定浓度范围内和聚(乙二醇)(PEG)分子质量范围内(2000,8000 ,and 20000 Da)的水合作用动力学的时间尺度与散装水(D 2O)。众所周知,PEG可以建立高度稳定的水合壳,因为相邻的醚氧之间的间距几乎与水的氢键网络相匹配。尽管这些第一壳水分子可能会显着滞后,但它们为后续的水合壳提供了界面,从而减少了对水定向动力学的主要熵扰动。除了更长的PEG外,使用PEG-400水溶液进行的一系列浓度依赖性2D-IR测量还显示出在临界重叠浓度附近的水合作用明显放缓(c*)。这些动力学结果与先前报道的PEG-1000水溶液的稳态红外光谱的比较表明,每个环氧乙烷单体对水分子数量的依赖程度惊人,完全取决于临界重叠浓度。
更新日期:2017-11-14
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